1. Technical Field of the Invention
The present invention relates to a frame phase synchronous system for adjusting phase synchronization between respective nodes such as relay nodes, switching nodes and base station nodes in a digital mobile communications system and, more particularly, to a frame phase synchronous system for measuring a frame phase difference by using a loop-back function of an ATM (ASYNCHRONOUS TRANSFER MODE) cell and independently matching the frame phases between the individual nodes.
2. Description of the Related Art
As a system for matching the frame synchronization between the nodes within the network, there is a master-slave synchronous system for realizing frequency synchronization between a master device and a slave device, wherein the master device transmits a transmission signal which is synchronized with a reference frequency of a reference clock in the master device, and the slave device extracts a clock signal from the received transmission signal and makes an oscillator of the device itself synchronized in phase with it.
Further, there is a mutual synchronous system which measures phase differences between own node and all other nodes and transfers the measuring results to other nodes, thus obtaining an average of the phase differences between all nodes, then setting this average to the frame phase of the own node, and thereby making the frame phase synchronization.
In a conventional digital mobile communications system, a master-slave synchronous system is applied in which a master node supplies a frame phase synchronous signal to switching nodes and base station nodes in the network via an STM (SYNCHRONOUS TRANSFER MODE) network. There arises, however, such a problem that a synchronizing accuracy can not be set to under 125 xcexcsec. at the minimum in terms of such a condition that the STM network be used. This is because it is prescribed in the STM network that the synchronization is executed by using one bit determined in one time slot, and hence the synchronizing accuracy can not be set to a one time slop length (125 xcexcsec.) or under.
Further, it is required in the mutual synchronous system that a path for matching the time be formed for all the nodes, and a device for calculating the phase difference is also needed, resulting in such a problem that the construction of each node becomes intricate.
A frame phase synchronous system according to the present invention is characterized by having the following constructions in order to solve the problems described above.
A frame phase synchronous system for adjusting phase synchronization in a digital mobile communications system comprises: a relay node which measures a frame phase difference with respect to other relay nodes using a method of calculating a frame phase difference from a propagation delay time through ATM cell loop-back, also obtains an optimum shift value as a first shift value for adjusting the phase synchronous in the relay node, and for notifies the first shift value to a switching node connected to as a slave; a switching node which measures a frame phase difference with respect to the host relay node and a frame phase difference with respect to a base station node as the slave, obtains a second shift value by adding the notified first shift value to a shift value derived from the measured frame phase difference with respect to the host relay node for adjusting the phase synchronous in the switching node, and also obtains a third shift value by adding the second shift value to a shift value derived from the measured frame phase difference with respect to the base station node as the slave for notifying the third shift value to the base station node; and a base station node which adjusts the phase synchronous by the third shift value notified by the host switching node.
Also, the relay node further comprises: a first frame phase difference adjusting unit which measures a frame phase difference with respect to other relay nodes, and obtains an optimum shift value as a first shift value for adjusting the phase synchronous in the relay node; and a first shift value notifying unit which notifies the first shift value to the switching node accommodated as a slave.
The switching node further comprises: a frame phase difference measuring unit which measures a frame phase difference with respect to the host relay node and a frame phase difference with respect to the base station node as the slave; a second frame phase difference adjusting unit which obtains a second shift value by adding the notified first shift value to a shift value derived from the measured frame phase difference with respect to the host relay node for adjusting the phase synchronous in the switching node; and a third frame phase difference adjusting unit which obtains a third shift value by adding the second shift value to a shift value derived from the measured frame phase difference with respect to the base station node accommodated as the slave for notifying the third shift value as an shift value to be adjusted in the base station node.
A method of frame phase synchronous in a digital mobile communications system, in which a plurality of relay nodes, switching nodes as slave nodes of the relay node, and base station nodes as slave nodes of the switching node are provided, according to the present invention is characterized by having the following constructions:
(1) measuring a frame phase difference, in the relay node, with respect to other relay nodes using a method of calculating a frame phase difference from a propagation delay time through ATM cell loop-back;
(2) obtaining an optimum shift value as a first shift value for adjusting the phase synchronous in the relay node;
(3) notifying the first shift value from the relay node to a switching node connected as a slave;
(4) measuring a frame phase difference, in the switching node, with respect to the host relay node and a frame phase difference with respect to a base station node as the slave using a method of calculating a frame phase difference from a propagation delay time through ATM cell loop-back;
(5) obtaining a second shift value, in the switching node, by adding the notified first shift value to a shift value derived from the measured frame phase difference with respect to the host relay node for adjusting the phase synchronous in the switching node;
(6) obtaining a third shift value, in the switching node, by adding the second shift value to a shift value derived from the measured frame phase difference with respect to the base station node as the slave for notifying of the third shift value the base station node; and
(7) adjusting the phase synchronous, in said base station node, by the third shift value notified by the host switching node.